The present invention relates to a pressure cap for a stationary filler neck of a tank, in particular a motor-vehicle radiator, according to the generic part of Claim 1.
In known pressure caps, for example for motor-vehicle radiators, the valve body of the valve arrangement is loaded in a constant manner in such a way that the flow connection between the inside and the outside of the radiator is opened when the pressure inside the radiator exceeds a certain threshold value. This then causes the air containing coolant to escape, Such simple pressure caps facilitate pressure equalization during operation of the motor vehicle when the pressure rises due to heating of the coolant in the radiator and when a critical pressure is exceeded. This is a safety aspect. However, in motor-vehicle radiators, overpressure due to accumulated heat also rises when the vehicle is not running, i.e. when the engine is turned off, and with the above named simple pressure caps, the valve arrangement is also opened completely, which poses the danger that a large amount of coolant escapes or evaporates, or that the radiator may even boil until empty, which means that coolant has to be replenished often. For that purpose, multi-stage pressure caps have been developed (DE 41 07 535 C1) which reduce the overpressure produced by accumulated heat differently than a considerably higher overpressure caused by malfunctioning. However, such a pressure cap is relatively expensive because it contains several contra-rotating valve-body parts and several sealing and counter-sealing surfaces. Furthermore, coolant is spilled in case of overpressure after the vehicle engine is turned off and the pressure is reduced. In that case, an absolute loss of water can be prevented only if an equalizing tank is provided to catch the liquid, or if an additional circulating pump is used which prevents the pressure from rising by circulating the coolant when the engine is turned off. However, this is expensive.
It is therefore the objective of the present invention to create a pressure cap of the type mentioned above, which on the one hand simply and cost-effectively prevents the opening due to overpressure produced by accumulated heat, and which on the other hand ensures that the tank is protected when the pressure rises further.
This objective is reached with a pressure cap of the type mentioned above which has the characteristics named in the detailed description.
The measures according to the invention achieve that the pre-stress exerted on the valve body can be controlled in such a way, depending, for example, on the operation of the motor vehicle, that the pressure cap does not open in case of a defined rate of overpressure produced by accumulated heat. This prevents the escape of air mixed with coolant during that xe2x80x9coperating phasexe2x80x9d. Additional components such as equalizing tanks or circulating pumps are not required. Overpressure can be reached by cooling the vehicle""s radiator during standstill. However, the pressure cap will open while the pressure rises above a certain safety threshold, to ensure that the cooling system is not damaged by bursting or leakages including the connector hoses. For example, the pre-stress means can be adjusted to two stages, i.e. to an opening pressure according to normal operation and a higher opening pressure which responds to pressure increase in case of accumulated heat.
The pre-stress means for the valve body can be controlled in various ways, according to the characteristics named in the detailed description. If the pre-stress means is controlled by negative pressure or overpressure, the set point can be picked up directly from the engine compartment of Otto engines or diesel engines. On the other hand, if an electrical signal is to be provided, it can be directly triggered, for example, when the ignition is on.
A preferred design for the pre-stress means of the valve body results from the characteristics named in the detailed description.
The power between the drive and the pressure piece [Druckstxc3xcck] can be transmitted either directly or via a power transmission element, i.e. a type of transmission gear. Furthermore, it is possible to have a straight-line connection or a connection via an element reversing the drive direction. Preferred designs of the element reversing the drive direction are named in the detailed description.
The type and design of the drive can also vary, as is shown by the characteristics in the detailed description.
In a particularly advantageous way, the drive can be accommodated in the cover handle. A combination of the pressure cap and a safety device to prevent release at excess temperature is apparent from the detailed description.
Further details of the invention are described below, where the invention is described with reference to the embodiments shown in the drawings. The drawings show: